Nitride semiconductor light emitting device array

ABSTRACT

A nitride semiconductor light emitting device array, which includes a dielectric layer formed on a first conductivity lower nitride semiconductor layer, having a plurality of windows. Each of a plurality of hexagonal pyramid light emission structures is grown from a surface of the first conductivity lower nitride semiconductor layer exposed through each of the windows and onto a peripheral area of the window of the dielectric layer. Each of the hexagonal pyramid light emission structures includes a first conductivity upper nitride semiconductor layer, an active layer and a second conductivity nitride semiconductor layer formed in their order. The windows are disposed in such a triangular arrangement that side surfaces of the adjacent hexagonal pyramid light emission structures face each other. Also, a distance between bases of the adjacent hexagonal pyramid light emission structures is less than 0.3 times an interval between centers of the windows of the adjacent hexagonal pyramid light emission structures.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. application Ser. No.11/819,785, filed on Jun. 29, 2007, now abandoned which claims thebenefit of Korean Patent Application No. 2006-0060699 filed on Jun. 30,2006, in the Korean Intellectual Property Office, the disclosures ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light emitting device array and, moreparticularly, to a light emitting device array having a plurality ofhexagonal pyramid light emitting structures formed by selective growth.

2. Description of the Related Art

Recently, researches have been actively conducted on semiconductor lightemitting devices as a new light source that can replace filament-basedlight bulbs and fluorescent lamps. In particular, the researches onlight emitting diodes (LEDs) using nitride compound semiconductors suchas GaN have been gaining attention. Without a suitably compatiblesubstrate, however, nitride crystals tend to have many crystal defects.

To remedy such problems, there has been suggested a method providing ahigh quality nitride light emitting device by forming hexagonalpyramid-shaped light emitting structures by selective growth.

FIG. 1 is a sectional view illustrating a conventional hexagonal pyramidshaped light emitting device.

As shown in FIG. 1, a dielectric layer 14 having a window W is formed ona first conductivity lower nitride semiconductor layer 12 a formed on asapphire substrate 11. A first conductivity upper nitride semiconductorlayer 12 b, an active layer 15, and a second conductivity nitridesemiconductor layer 16 are grown in the window W by a lateral growthprocess utilizing the dielectric layer 14. At this time, the nitridesemiconductor layers 12 b, 15 and 16 are grown in the window W to form ahexagonal pyramid shaped light emitting structure. One of a transparentconductive thin film 17 and an electrode 19 is fanned on the secondconductivity nitride semiconductor layer 16 of the hexagonal pyramidlight emitting structure, and a part of the dielectric layer is etchedto expose a surface of the first conductivity lower nitridesemiconductor layer 12 a and form another electrode 18 of differentpolarity.

It has been reported that a large number of defects, growing in ahorizontal direction, in the nitride single crystals obtained by theselective growth, are blocked or change direction in the process oflateral growth, thus rarely affecting the active layer. Also, since theeffect of lattice mismatch between the nitride single crystals and asubstrate is insignificant, the crystal growth defects may be decreased.

In such an LED structure, a hexagonal pyramid structure has asubstantial light emission area enlarged by the inclined side surfacesthereof and the piezoelectric field effect may also be mitigated by thecrystal growth direction.

In addition, in order to obtain superior luminance, the hexagonalpyramid light emission structure shown in FIG. 1 is provided in aplurality arranged in an array. For optimal space utilization, thewindows of the hexagonal pyramid light emitting devices are disposed ina triangular arrangement. However, as shown in FIG. 2, in an equilateraltriangular arrangement of windows, even if the hexagonal pyramid lightemission structures 20 are grown to occupy a maximum area, a greatnumber of wasted areas A, which cannot be utilized as the light emissionarea, remain.

Therefore, there is a need for an arrangement of hexagonal pyramid lightemission structures in order to minimize the waste of space and maximizethe light emission area of a light emitting device.

SUMMARY OF THE INVENTION

An aspect of the present invention provides a nitride semiconductorlight emitting device array, which maximizes a light emission areaformed by a plurality of hexagonal pyramid light emission structures byimproving an arrangement of the hexagonal pyramid light emissionstructures and windows.

According to an aspect of the invention, there is provided a nitridesemiconductor light emitting device array including: a dielectric layerformed on a first conductivity lower nitride semiconductor layer andhaving a plurality of windows formed therethrough; and a plurality ofhexagonal pyramid light emission structures each selectively grown froma surface of the first conductivity lower nitride semiconductor layerexposed through each of the windows and onto a peripheral area of thewindow of the dielectric layer, each of the hexagonal pyramid lightemission structures comprising a first conductivity upper nitridesemiconductor layer, an active layer and a second conductivity nitridesemiconductor layer formed in their order, wherein the plurality ofwindows are disposed in a triangular arrangement such that side surfacesof one of the hexagonal pyramid light emission structures face sidesurfaces other adjacent ones of the hexagonal pyramid light emissionstructures, and wherein a distance from a base of one of the hexagonalpyramid light emission structures to a base of another adjacent one ofthe hexagonal pyramid light emission structures is less than 0.3 timesan interval from a center of the window of one of the hexagonal pyramidlight emission structures to a center of the window of another adjacentone of the hexagonal pyramid light emission structures.

The side surface of each of the hexagonal pyramid light emissionstructure may be in [11-20] direction. Also, a sum of side surface areasof the plurality of hexagonal pyramid light emission structures may begreater than a total growth surface area of the dielectric layer.

To obtain a substantially maximum light emission area under an optimalarrangement condition, adjacent ones of the hexagonal pyramid lightemission structures may be arranged to abut each other at bases thereof.

In the exemplary embodiments of the present invention, a horizontalstructure as well as a vertical structure light emitting device may berealized in terms of electrode arrangement.

A horizontal-structure nitride semiconductor light emitting device arrayaccording to an embodiment further includes a substrate having the firstconductivity lower nitride semiconductor layer formed thereon; a firstelectrode formed on a surface of the first conductivity lower nitridesemiconductor layer; a light-transmitting conductive layer formed on thesecond conductivity nitride semiconductor layer; and a second electrodeformed on a surface of the light transmitting conductive layer. In thiscase, the substrate may be one selected from the group consisting of asapphire substrate, a SiC substrate and a Si substrate.

A vertical-structure nitride semiconductor light emitting device arrayaccording to another embodiment may further include a light-transmittingconductive layer with the first conductivity lower nitride semiconductorlayer formed thereon; a first electrode formed on a surface of thelight-transmitting conductive layer; a reflective electrode layer formedon the second conductivity nitride semiconductor layer; and a conductivesupport structure formed on the reflective electrode layer to functionas a second electrode. In particular, in the vertical structure lightemitting device array according to the present invention, sincereflecting layers are formed on the upper surfaces of the hexagonalpyramid light emitting structure, light is focused and extracted throughthe first conductivity lower nitride semiconductor layer, therebysignificantly improving the light extraction efficiency.

According to another aspect of the invention, there is provided anitride semiconductor light emitting device array including: adielectric layer formed on a first conductivity lower nitridesemiconductor layer and having a plurality of windows formedtherethrough at a predetermined interval in rows and columns in arectangular arrangement; and a plurality of hexagonal pyramid lightemission structures each selectively grown from a surface of the firstconductivity lower nitride semiconductor layer exposed by each of thewindows and onto a peripheral portion of each of the windows of thedielectric layer, each of the hexagonal pyramid light emission structurecomprising a first conductivity upper nitride semiconductor layer, anactive layer and a second conductivity nitride semiconductor layerformed in their order, wherein one of the hexagonal pyramid lightemission structures has at least one base abutting at least one base ofat least one other adjacent hexagonal pyramid light emission structuredisposed in one direction of rows and columns, and has at least one edgefacing at least one edge of other adjacent ones of the hexagonal pyramidlight emitting structures disposed in the other direction of rows andcolumns.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a sectional view illustrating a conventional hexagonal pyramidnitride light emitting device;

FIG. 2 is a schematic view illustrating a conventional hexagonal pyramidnitride light emitting device array;

FIG. 3 is a schematic plan view illustrating a hexagonal pyramid nitridelight emitting device array according to an embodiment of the presentinvention;

FIG. 4 is a graph showing the side surface utilization ratio accordingto the spatial relationship of the hexagonal pyramid structures;

FIG. 5 is a schematic view illustrating a hexagonal pyramid nitridelight emitting device array according to an embodiment of the presentinvention;

FIG. 6 is a schematic view illustrating a hexagonal pyramid nitridelight emitting device array according to another embodiment of thepresent invention; and

FIGS. 7( a) and 7(b) are sectional views illustrating the hexagonalpyramid nitride light emitting device according to the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Exemplary embodiments of the present invention will now be described indetail with reference to the accompanying drawings.

FIG. 3 is a schematic plan view illustrating a hexagonal pyramid nitridelight emitting device array according to an embodiment of the presentinvention.

FIG. 3 illustrates a light emitting device array with hexagonal pyramidnitride light emission structures 30 grown on a dielectric layer 34 witha plurality of windows W formed therethrough. As described herein withreference to FIG. 1, each of the hexagonal pyramid nitride lightemission structure 30 may be understood as including a firstconductivity upper nitride semiconductor layer, an active layer and asecond conductivity nitride semiconductor layer selectively grown in thewindow W.

For an optimal arrangement of the hexagonal pyramid nitride lightemission structures 30 according to the present invention, the pluralityof windows W are disposed in an equilateral triangular arrangement,which is regularly repeated. In particular, the windows W are arrangedin such away that side surfaces 30 a of the adjacent hexagonal pyramidlight emission structures 30 face each other. Such an arrangement inwhich the side surfaces 30 a of the adjacent hexagonal pyramid lightemission structures 30 face each other may be obtained by suitablyadjusting the locations of the windows in the equilateral triangulararrangement in consideration of the crystal direction. The windows W maybe suitably arranged so that, for example, the side surface 30 a of eachof the hexagonal pyramid light emission structures 30 may be in [11-20]direction, and the side edge may be in [1-100] direction. That is, withrespect to a specific window, another adjacent window is disposed in alocation predicted as [11-20] crystal growth direction of the specificwindow. The crystal growth direction may be predicted from the crystalsurface being grown.

As described above, when the side surfaces 30 a of the adjacenthexagonal pyramid light emission structures 30 face each other, thelight emission area can be maximized. Also, the area occupied by thehexagonal pyramid light emission structures 30 may be maximized in orderto increase the light emission area in such an arrangement of thewindows W. The hexagonal pyramid light emission structures 30 may beformed in a large size so that a distance X between the adjacenthexagonal pyramid light emission structures 30 is 0.3 times less than aninterval between the centers of the window areas of the adjacenthexagonal pyramid light emission structures 30. This allows effectiveincrease of the light emission area, based on the window arrangementstructure according to the present invention.

The area occupied by the plurality of hexagonal pyramid light emissionstructures 30 as described above may be designed so that a substantiallight emission area, i.e., a total area of the side surfaces 30 a of thehexagonal pyramid light emission structures, is larger than a total areaof the dielectric layer 34. This condition can be derived from a sidesurface utilization ratio, based on a cosine value of an inclinationangle of the hexagonal pyramid light emission structure.

FIG. 4 shows the side surface utilization ratio, i.e., the ratio of aninterval a between the centers of the adjacent windows to a distance Xbetween the side surfaces, at 62°, which is the inclination angle of theside surface 30 a of the hexagonal pyramid light emission structure foroptimization of piezoelectric effect. In this case, “the side surfaceutilization ratio” designates a ratio of a total sum of the side surfaceareas of all of the hexagonal pyramid light emission structures to anentire substrate (dielectric layer) area. The utilization ratio of 1indicates that the total sum of the side surface areas is equal to theentire substrate (dielectric layer) area, and the utilization ratiogreater than 1 indicates that the light emission area is substantiallygreater than the substrate (dielectric layer) area.

In the graph of FIG. 4, it can be seen that when a distance between theside surfaces is 0.3 with respect to an interval between the centers ofthe windows, the substantial light emission area (i.e., the sum of theside surfaces of the light emission structures) is almost equal to thearea of the substrate (dielectric layer). On the other hand, when thedistance is less than 0.3, the substantial light emission area is largerthan the area of the substrate (dielectric layer). Therefore, asdescribed hereinabove, even if the windows are disposed in anequilateral triangular arrangement where the side surfaces of theadjacent light emission structures face each other, the light emissionstructures are required to be grown such that the distance between theside surfaces is less than 0.3 times the interval between the centers ofthe windows, in order to increase the substantial light emission area.This may be translated to a condition in which, the sum of the sidesurface areas of the plurality of hexagonal pyramid light emissionstructures is greater than the total growth area of the dielectriclayer.

Therefore, the light emitting device array shown in FIG. 5 ensures amaximum light emission area in an optimal window W arrangementcondition. Each of the plurality of hexagonal pyramid light emissionstructures 50 may be grown in a large size so that the side surfaces 50a face each other and the bases abut each other, thereby ensuring alight emission area more than two times an area of the substrate(dielectric layer).

In an alternative embodiment, the light emission structures may bearranged with a high side surface utilization ratio by employing thewindow arrangement shown in FIG. 6.

As shown in FIG. 6, a plurality of windows W are formed in thedielectric layer at a predetermined interval in rows X and columns Y. Inaddition, the plurality of hexagonal pyramid light emission structures50 are arranged such that the side surfaces 50 a of the adjacent lightemission structures face each other in one direction of rows X andcolumns Y, while at the same time, the edges 50 b of the adjacent lightemission structures abut each other in the other direction of rows X andcolumns Y.

Under this configuration, each of the light emission structures aregrown in a large size so that the lower ends of the side surfaces andthe edges across from each other may abut each other, thereby maximizingthe area efficiency. In this case, when the inclination angle of theside surface is 62°, a light emission area about 1.60 times larger thanthe substrate area can be obtained from the side surfaces of thehexagonal pyramids.

The method of maximizing the light emission area according to thepresent invention may be advantageously applied to a horizontalstructure as well as a vertical structure light emitting device.

FIGS. 7( a) and 7(b) are sectional views illustrating a hexagonalpyramid nitride light emitting device according to the presentinvention.

Referring to FIG. 7( a), a horizontal structure light emitting device 70according to an embodiment of the present invention includes a substrate71 with a first conductivity lower nitride semiconductor layer 72 aformed thereon. In this case, the substrate may be one selected from asapphire substrate, a SiC substrate and a Si substrate.

A dielectric layer 74 with a plurality of windows formed therethrough isformed on the first conductivity lower nitride semiconductor layer 72 a.On the surfaces of the first conductivity lower nitride semiconductorlayer 72 a exposed by the windows, a first conductivity upper nitridesemiconductor layer 72 b, an active layer 75 and a second conductivitynitride semiconductor layer 76 are sequentially grown to provide aplurality of hexagonal pyramid light emission structures. The pluralityof windows and the hexagonal pyramid light emission structures may bearranged as shown in FIGS. 3. 5 and 6 to maximize the effective lightemission area.

As shown in FIG. 7( a), a first electrode 78 is formed on a surface ofthe first conductivity lower nitride semiconductor layer 72 a. Alight-transmitting conductive layer 77 is formed on the secondconductivity nitride semiconductor layer 76, and a second electrode 79is formed on a surface of the light-transmitting conductive layer 77.

Alternatively, FIG. 7( b) illustrates a vertical structure lightemitting device according to another embodiment of the presentinvention.

As shown in FIG. 7( b), a dielectric layer 84 with a plurality ofwindows formed therethrough is formed on a first conductivity lowernitride semiconductor layer 82 a. On surfaces of the first conductivitylower nitride semiconductor layer 82 a exposed by the windows, a firstconductivity upper nitride semiconductor layer 82 b, an active layer 85and a second conductivity nitride semiconductor layer 86 aresequentially formed to provide a plurality of hexagonal pyramid lightemission structures.

In the vertical structure light emitting device array shown in FIG. 7(b), a reflective electrode 87 may be made of a metal such as Ag on thesecond conductivity nitride semiconductor layer 86. In addition, inorder to support the remaining portion of the light emitting device whenthe growth substrate such as a sapphire substrate, for growing thenitride single crystal light emitting device, is removed and to providean electrically connected structure, a conductive support structure 89may be formed on the reflective electrode layer 87 by a metal platingmethod. Such a conductive support structure 89 may be formed to have aplanar surface by plating with one of Ni and Cu to fill the spacesbetween the pyramid light emission structures. Such a conductive supportstructure 89 may be used as a lower electrode in a packaging process.

Next, the growth substrate such as a sapphire substrate is removed byone of laser lift-off and chemical etching. In order for uniform supplyof current to the surface separated from the sapphire, alight-transmitting conductive layer 88 may be deposited thereon.

In the vertical structure light emitting device shown in FIG. 7( b),with the reflective layer formed on the hexagonal pyramid light emissionstructure, light is concentrated to be extracted through the firstconductivity lower nitride semiconductor layer, thereby advantageouslyimproving light extraction efficiency. This effectively enhances lightefficiency due to the increased light emission area.

According to the present invention as set forth above, hexagonal pyramidlight emission structures grown with very few crystal defects byselective growth are arranged to occupy a large area as possible,thereby increasing a substantial light emission area. This is applied toa vertical structure light emitting device to provide a nitride lightemitting device array with high light extraction efficiency.

While the present invention has been shown and described in connectionwith the exemplary embodiments, it will be apparent to those skilled inthe art that modifications and variations may be made without departingfrom the spirit and scope of the invention as defined by the appendedclaims.

What is claimed is:
 1. A nitride semiconductor light emitting device array comprising: a dielectric layer formed on a first conductivity lower nitride semiconductor layer and having a plurality of windows formed therethrough; a plurality of hexagonal pyramid light emission structures each selectively grown from a surface of the first conductivity lower nitride semiconductor layer exposed through each of the plurality of windows and onto a peripheral area of the plurality of windows of the dielectric layer, each of the hexagonal pyramid light emission structures comprising a first conductivity upper nitride semiconductor layer, an active layer and a second conductivity nitride semiconductor layer formed in this order; a reflective electrode formed on the plurality of hexagonal pyramid light emission structures respectively to be contacted with the second conductivity nitride semiconductor layer; and a conductive support structure formed on the reflective electrode layer and filling spaces between the plurality of hexagonal pyramid light emission structures to provide a substantially planar surface, wherein the plurality of windows are disposed in a grid such that centers of adjacent windows are disposed in perpendicular rows and columns, and wherein a predetermined interval spacing between adjacent rows and columns is such that two opposing side surfaces of one of the plurality of hexagonal pyramid light emission structures abut side surfaces of other adjacent ones of the plurality of hexagonal pyramid light emission structures, and wherein a sum of side surface areas of the plurality of hexagonal pyramid light emission structures is greater than a total growth surface area of the dielectric layer.
 2. The nitride semiconductor light emitting device array according to claim 1, wherein the side surface of each of the plurality of hexagonal pyramid light emission structure is in [11-20] direction.
 3. The nitride semiconductor light emitting device array according to claim 1, wherein side surfaces of the hexagonal pyramid light emission structures having inclination angles of approximately 62°.
 4. The nitride semiconductor light emitting device array according to claim 1, further comprising: a light-transmitting conductive layer formed over a surface of the first conductivity lower nitride semiconductor layer, wherein the surface having the light-transmitting conductive layer formed thereon is a surface opposite to a surface having the dielectric layer formed thereon, and wherein the light-transmitting conductive layer is formed over the surface of the first conductivity lower nitride semiconductor layer so as to provide a uniform supply of current to the nitride semiconductor light emitting device array.
 5. A nitride semiconductor light emitting device array comprising: a dielectric layer formed on a first conductivity lower nitride semiconductor layer and having a plurality of windows formed therethrough at a predetermined interval; a plurality of hexagonal pyramid light emission structures each selectively grown from a surface of the first conductivity lower nitride semiconductor layer exposed by each of the plurality of windows and onto a peripheral portion of each of the plurality of windows of the dielectric layer, each of the plurality of hexagonal pyramid light emission structure comprising a first conductivity upper nitride semiconductor layer, an active layer and a second conductivity nitride semiconductor layer formed in this order; a reflective electrode formed on the plurality of hexagonal pyramid light emission structures respectively to be contacted with the second conductivity nitride semiconductor layer; and a conductive support structure formed on the reflective electrode layer and filling spaces between the plurality of hexagonal pyramid light emission structures to provide a substantially planar surface, wherein the windows formed through the dielectric layer are disposed in a grid such that centers of adjacent windows are disposed in perpendicular rows and columns, and wherein a predetermined interval spacing between adjacent rows and columns is such that one of the plurality of hexagonal pyramid light emission structures has at least one base abutting at least one base of at least one other adjacent hexagonal pyramid light emission structure disposed in one direction of rows and columns, and has at least one edge facing at least one edge of other adjacent ones of the plurality of hexagonal pyramid light emitting structures disposed in the other direction of rows and column, and wherein a sum of side surface areas of the plurality of hexagonal pyramid light emission structures is greater than a total growth surface area of the dielectric layer.
 6. The nitride semiconductor light emitting device array according to claim 5, wherein side surfaces of the hexagonal pyramid light emission structures having inclination angles of approximately 62°.
 7. The nitride semiconductor light emitting device array according to claim 5, further comprising: a light-transmitting conductive layer formed over a surface of the first conductivity lower nitride semiconductor layer, wherein the surface having the light-transmitting conductive layer formed thereon is a surface opposite to a surface having the dielectric layer formed thereon, and wherein the light-transmitting conductive layer is formed over the surface of the first conductivity lower nitride semiconductor layer so as to provide a uniform supply of current to the nitride semiconductor light emitting device array. 